| Zone / Room | Area (m²) | Heat Loss (W) | Max Loop (m) | Zone Type | |
|---|---|---|---|---|---|
| Total Area: 0 m² | Total Load: 0 W | Flow: - | |||
Per-Zone Design Schedule
Complete Zone Schedule
| Zone | Heat Loss | Heat Flux | Tube Spacing | Loop Length | Flow Rate | Floor Temp |
|---|
How to Use the Radiant Floor Heat Calculator
The construction type sets the thermal resistance between the PEX tube and the floor surface. A concrete slab has the lowest resistance, transferring heat efficiently. Staple-up systems under a wood subfloor have higher resistance, especially without aluminium heat-transfer plates. Higher construction resistance means you need a higher supply water temperature or tighter tube spacing to deliver the same heat flux.
Floor covering R-value is the single biggest variable in radiant floor design. Tile and polished concrete have virtually zero added resistance and allow maximum heat transfer. Thick carpet can block so much heat that radiant floor can't deliver enough output without raising supply temperatures above comfort limits. Engineered hardwood is a good compromise - better thermal performance than solid wood and more dimensionally stable under the temperature cycling of a radiant system.
Enter supply and return water temperatures for the radiant system. Typical residential radiant systems run at 35–55°C supply and 25–45°C return, making them an ideal match for condensing boilers and heat pumps. The mean water temperature (MWT = (supply + return) / 2) drives the heat output calculation. A lower MWT with the same floor construction needs either tighter tube spacing or a higher supply temperature to meet the zone load.
Enter one row per zone or room with floor area, design heat loss, maximum loop length, and zone type. Heat loss comes from a room-by-room heat loss calculation - use our heat load calculator. Maximum loop length is typically 90–120 m for 12mm PEX and up to 150 m for 16mm PEX to keep pressure drop manageable. Zone type (standard, perimeter, or bathroom) adjusts the floor surface temperature limit used in the comfort check.
The results show tube spacing, number of loops, total PEX length, flow rate, and floor surface temperature for each zone. Check the surface temperature against the comfort limits - 29°C for occupied areas, 33°C for bathrooms. The total flow rate and boiler load are used to size the boiler with the boiler sizing calculator and the system curve with the system curve calculator.
Designing Hydronic Radiant Floor Heating for Canadian Buildings
Radiant floor heating is one of the most comfortable and energy-efficient space heating methods available for Canadian homes. When properly designed, it delivers even heat across the entire floor surface, eliminates drafts, and operates at water temperatures low enough for condensing boilers and heat pumps to work at peak efficiency.
How Radiant Floor Heat Transfer Works
A hydronic radiant floor delivers heat by two mechanisms: radiation directly from the warm floor surface to cooler room surfaces and occupants, and natural convection of warm air rising from the floor. At typical floor temperatures of 25–28°C, about 50–60% of the heat transfer is radiant and the rest is convective. This is warmer at foot level and cooler at head level - the opposite of a forced-air system - which is why radiant floor heating feels comfortable at lower air temperatures than convective systems. Most Canadians find radiant floor rooms comfortable at 20°C air temperature where they'd want 22°C with forced air.
The Design Equation
Heat flux from a radiant floor in W/m² depends on the mean water temperature (MWT), room air temperature, total thermal resistance from water to room air (R-total), and tube spacing. R-total = R-construction (slab + tube) + R-covering + R-air film (approximately 0.13 m²K/W). Heat flux = (MWT − Troom) / R-total. Required tube spacing = (heat flux at that MWT) / (heat loss per m²). This calculator applies this formula for each zone, then checks the resulting floor surface temperature against comfort limits.
Floor Surface Temperature Limits
ASHRAE 55 limits occupied floor surface temperatures to 29°C (84°F) for sedentary occupancies and 33°C (91°F) for bathrooms where bare feet tolerate warmth better. Perimeter zones near exterior walls and below large windows are sometimes designed to 35°C. Exceeding these limits doesn't just cause discomfort - it can damage hardwood floors and, at extreme temperatures, be a burn risk for seated or crawling occupants. The calculator flags any zone whose resulting floor surface temperature exceeds the limit for its zone type.
Tube Spacing and Loop Length
Standard tube spacings in Canadian practice are 100, 150, 200, 250, and 300 mm (4, 6, 8, 10, 12 inches) on centre. The tightest spacing, 100 mm, is used for high-heat-loss perimeter zones. Interior zones in well-insulated new construction often work at 200–300 mm. Maximum loop length is limited by pressure drop: for 12mm PEX at typical flow rates, loops over 90–100 m start to have excessive pressure drop and uneven temperature distribution. 16mm PEX extends this to 120–150 m. Keeping loops under these limits and balancing loop lengths within a manifold zone avoids flow imbalance problems.
Radiant Floor and Condensing Boilers in Canada
Radiant floor systems are the ideal partner for condensing boilers and air-to-water heat pumps. A concrete slab system with tile covering can deliver full comfort at 40–45°C supply water, with return temperatures of 30–35°C - well below the 55°C threshold where condensing stops. This means the boiler operates in full condensing mode throughout the Canadian heating season, consistently achieving AFUE above 95%. Compare this to a baseboard system where supply must be 70–82°C to deliver rated output, pushing the boiler out of condensing mode entirely. The condensing boiler calculator quantifies the efficiency difference.
Slab Insulation Requirements in Canada
The National Building Code of Canada requires slab-on-grade insulation in most climate zones. For a heated slab, the insulation goes below and around the perimeter of the slab to prevent heat from migrating into the ground rather than into the room. Without adequate under-slab insulation, a radiant slab wastes a significant fraction of its heat to the ground - both an energy and a comfort problem. The minimum recommendation for Canadian conditions is RSI-2.0 (R-11) under the full slab area and RSI-3.5 (R-20) at the perimeter extending down to the frost depth. Colder provinces like Alberta, Manitoba, and Saskatchewan warrant higher values.
Manifold Design and Balancing
All loops in a radiant zone connect at a manifold. Good manifold design keeps loop lengths within 15% of each other across a manifold, uses individual flow meters on each loop for balancing, and includes isolation valves for future servicing. Use our primary-secondary piping calculator for multi-zone systems with multiple manifolds. Each manifold zone should have its own zone valve or circulator so unoccupied areas can be reduced to setback temperature without affecting other zones.
Frequently Asked Questions
Tube spacing ranges from 100 mm (4 inches) for high-loss perimeter zones to 300 mm (12 inches) for well-insulated interior zones. The right spacing depends on your zone heat loss per m², floor covering R-value, slab type, and supply water temperature. Tighter spacing gives more output but costs more tubing and installation time. This calculator determines the correct spacing for each zone automatically. For most Canadian new construction with good insulation, 200 mm spacing at 40–45°C supply works well for the bulk of the floor area, with 150 mm near exterior walls and large windows.
ASHRAE limits occupied floor surface temperature to 29°C (84°F) for areas where people stand or sit for extended periods - living rooms, offices, bedrooms. Bathroom floors can go to 33°C (91°F). Perimeter zones are sometimes designed to 35°C. Exceeding 29°C causes feet to feel uncomfortably hot before the room air reaches design temperature. It can also damage solid hardwood floors and, over time, dry out engineered wood. This calculator checks the resulting floor surface temperature for every zone and flags those that exceed the comfort limit for the zone type selected.